using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// Covers <see cref="MotionSequenceGate"/> — the inbound movement-event
/// staleness gate ported from retail (L.2g S1, deviation DEV-6):
///
/// <list type="bullet">
/// <item><c>CPhysicsObj::is_newer</c> (0x00451ad0) — the wraparound u16
///   timestamp compare (ACE <c>PhysicsObj.is_newer</c> confirms the
///   semantics; the BN pseudo-C return values are setcc-garbled).</item>
/// <item>The 0xF74C dispatch INSTANCE_TS gate
///   (<c>ACSmartBox::DispatchSmartBoxEvent</c>,
///   acclient_2013_pseudo_c.txt:357214-357239): stale incarnation → drop
///   BEFORE any movement stamp is touched.</item>
/// <item><c>CPhysics::SetObjectMovement</c> (0x00509690,
///   acclient_2013_pseudo_c.txt:271370): MOVEMENT_TS accepts only strictly
///   newer sequences and stamps BEFORE the server-control gate;
///   SERVER_CONTROLLED_MOVE_TS drops when the stored stamp is strictly
///   newer than the incoming one (equal passes).</item>
/// </list>
/// </summary>
public class MotionSequenceGateTests
{
    // CPhysicsObj::is_newer(old, new): abs(new-old) > 0x7fff ? new < old : old < new.
    [Theory]
    [InlineData((ushort)0, (ushort)1, true)]        // simple newer
    [InlineData((ushort)1, (ushort)0, false)]       // simple older
    [InlineData((ushort)5, (ushort)5, false)]       // equal is not newer
    [InlineData((ushort)0, (ushort)0x7FFF, true)]   // abs diff exactly 0x7fff → normal compare
    [InlineData((ushort)0, (ushort)0x8000, false)]  // abs diff 0x8000 → wraparound branch
    [InlineData((ushort)0xFFFF, (ushort)0, true)]   // 0 is newer than 0xFFFF (wrap)
    [InlineData((ushort)0xFFFE, (ushort)2, true)]   // newer across the seam
    [InlineData((ushort)2, (ushort)0xFFFE, false)]  // older across the seam
    public void IsNewer_MatchesRetailWraparoundCompare(ushort oldStamp, ushort newStamp, bool expected)
    {
        Assert.Equal(expected, MotionSequenceGate.IsNewer(oldStamp, newStamp));
    }

    [Fact]
    public void FirstEvent_WithFreshMovementSequence_IsAccepted()
    {
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(instanceSeq: 0, movementSeq: 1, serverControlSeq: 0));
    }

    [Fact]
    public void DuplicateMovementSequence_IsDropped()
    {
        // Gate 1 accepts strictly-newer only — an identical movementSeq is a
        // duplicate delivery, not a new command.
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(0, 5, 0));
        Assert.False(gate.TryAcceptMovementEvent(0, 5, 0));
    }

    [Fact]
    public void StaleMovementSequence_IsDropped_ThenNewerAccepted()
    {
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(0, 5, 0));
        Assert.False(gate.TryAcceptMovementEvent(0, 4, 0)); // reordered straggler
        Assert.True(gate.TryAcceptMovementEvent(0, 6, 0));
    }

    [Fact]
    public void MovementSequence_WrapsAroundTheU16Seam()
    {
        // Stamps live in u16 space and wrap; retail seeds them from the
        // CreateObject PhysicsDesc timestamp block, so a gate near the seam
        // must accept the post-wrap values as newer.
        var gate = new MotionSequenceGate();
        gate.Seed(instanceSeq: 0, movementSeq: 0xFFFD, serverControlSeq: 0);
        Assert.True(gate.TryAcceptMovementEvent(0, 0xFFFE, 0));
        Assert.True(gate.TryAcceptMovementEvent(0, 2, 0)); // 2 is newer than 0xFFFE by wrap rule
        Assert.False(gate.TryAcceptMovementEvent(0, 0xFFFE, 0)); // and the old stamp is now stale
    }

    [Fact]
    public void SeededGate_AcceptsNextSequence_RejectsThePast()
    {
        // The exact case zero-init would break: spawning near a long-lived
        // entity whose movement sequence is already past 0x8000. Retail
        // seeds update_times from CreateObject's PhysicsDesc timestamps
        // (ACE WorldObject_Networking.cs:411-420 writes all 9 in enum
        // order), so the first UM after spawn is judged against the
        // seeded stamp, not zero.
        var gate = new MotionSequenceGate();
        gate.Seed(instanceSeq: 3, movementSeq: 0x9000, serverControlSeq: 2);
        Assert.True(gate.TryAcceptMovementEvent(3, 0x9001, 2));
        Assert.False(gate.TryAcceptMovementEvent(3, 0x8FFF, 2)); // pre-spawn straggler
    }

    [Fact]
    public void Reseed_WithOlderStamps_DoesNotRegress()
    {
        // The #138 rehydrate path replays RETAINED CreateObject spawns
        // through the normal spawn handler (GameWindow.RehydrateServerEntities
        // ForLandblock) — re-seeding from that cached spawn must not roll the
        // live stamps backward, or a post-rehydrate straggler UM would be
        // accepted as fresh. First Seed adopts wholesale (fresh object);
        // later Seeds only advance.
        var gate = new MotionSequenceGate();
        gate.Seed(instanceSeq: 3, movementSeq: 0x9000, serverControlSeq: 2);
        Assert.True(gate.TryAcceptMovementEvent(3, 0x9001, 2));

        gate.Seed(instanceSeq: 3, movementSeq: 0x8000, serverControlSeq: 2); // stale replay
        Assert.False(gate.TryAcceptMovementEvent(3, 0x9001, 2)); // still a duplicate
        Assert.True(gate.TryAcceptMovementEvent(3, 0x9002, 2));

        gate.Seed(instanceSeq: 4, movementSeq: 0x9010, serverControlSeq: 2); // genuine re-create
        Assert.False(gate.TryAcceptMovementEvent(3, 0x9011, 2)); // old incarnation stale
        Assert.True(gate.TryAcceptMovementEvent(4, 0x9011, 2));
    }

    [Fact]
    public void StaleServerControl_Drops_ButMovementStampStillAdvances()
    {
        // Retail stamps MOVEMENT_TS BEFORE evaluating the server-control gate
        // (0x00509690: update_times[1] written at 0x005096dd, the SC compare
        // runs after) — a movement event dropped for stale server-control
        // still consumes its movement sequence.
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(0, 1, 5));
        Assert.False(gate.TryAcceptMovementEvent(0, 2, 4)); // sc=4 older than stored 5 → drop
        Assert.False(gate.TryAcceptMovementEvent(0, 2, 5)); // movementSeq 2 was consumed by the drop
        Assert.True(gate.TryAcceptMovementEvent(0, 3, 5));  // next movementSeq proceeds
    }

    [Fact]
    public void EqualServerControl_Passes()
    {
        // The SC gate drops only when the STORED stamp is strictly newer than
        // the incoming one; equal means "same server-control era" and applies.
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(0, 1, 7));
        Assert.True(gate.TryAcceptMovementEvent(0, 2, 7));
    }

    [Fact]
    public void StaleInstance_Drops_WithoutConsumingMovementSequence()
    {
        // The INSTANCE_TS gate runs at dispatch level, BEFORE
        // CPhysics::SetObjectMovement — a stale-incarnation event must not
        // touch the movement stamps.
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(2, 1, 0));
        Assert.False(gate.TryAcceptMovementEvent(1, 2, 0)); // stale incarnation
        Assert.True(gate.TryAcceptMovementEvent(2, 2, 0));  // seq 2 was NOT consumed by the instance drop
    }

    [Fact]
    public void NewerInstance_IsAdoptedAndApplied()
    {
        // DIVERGENCE (register row added with this port): retail queues the
        // blob until the newer incarnation exists (SmartBox::QueueBlobForObject,
        // dispatch return 4); acdream adopts the newer instance stamp and
        // applies immediately.
        var gate = new MotionSequenceGate();
        Assert.True(gate.TryAcceptMovementEvent(1, 1, 0));
        Assert.True(gate.TryAcceptMovementEvent(2, 2, 0));  // newer incarnation adopted
        Assert.False(gate.TryAcceptMovementEvent(1, 3, 0)); // old incarnation now stale
    }

    [Fact]
    public void InstanceCompare_WrapsAroundTheU16Seam()
    {
        var gate = new MotionSequenceGate();
        gate.Seed(instanceSeq: 0xFFFE, movementSeq: 0, serverControlSeq: 0);
        Assert.True(gate.TryAcceptMovementEvent(0xFFFE, 1, 0));
        Assert.True(gate.TryAcceptMovementEvent(2, 2, 0));  // instance 2 newer than 0xFFFE by wrap
    }
}